Fuel tank flush

[Scot]

Any suggestions as to how to do a basic flushing of the tanks of my Model 4 without removing the wings? The aircraft is on the trailer with fuselage level and fuel system completely emptied. I was planning to use some filtered 100LL measured into the wing tanks, with a length of fuel line attached to the barb but not run to the header tank. Slosh it around a bit, then drain into another measured clear container to inspect for debris or other contamination. Problem is, if I do this with the finger strainers in place, they will just catch any large bits of debris and keep them in the tank. More or less the same with the header tank, which I suspect has debris in it.

I don't really suspect any failure of the fiberglass, and inspection with a borescope done before purchase did not reveal anything alarming. To my knowledge the tanks have never had mogas in them, but upon servicing the gascolator recently, it was full of debris which was obviously drill shavings from the header tank, so I figure it would be prudent to just flush the entire system. Maybe someone out there has a good procedure?

[Dave S]

Hi Scot,

I think your procedure of flushing the wing tanks first is good. Your question about the finger strainers is valid - is there any way you can remove the finger strainers? I realize that can be a problem in some cases due to interference with the fuel elbow; but, if you can get them out I'd sure try it.

Curious on the header tank - does the plane have the original plastic tank? If there were plastic chips in the gascolator the header was probably not cleaned up very well when it was originally installed. My temptation would be to remove the header tank and its fittings to flush it and check for any additional chips that haven't come loose yet from the original drilling and tapping. If the fuel system is empty that should not take long to do.

FWIW - I have found that the bottom of the header tank is where dust and insect parts settle that enter the fuel system through the wing tank pitot openings. I have made a habit of removing the header tank at least once every 3 - 4 annual condition inspections to clean it up. The kitfox header tank works really well to settle out any stuff that happens to get through. I have never found very much but like to get it out.

Running the flush through a coffee filter works real well to figure out when everything is completely clean.

I am sure others will have some procedures that work well on your IV.

[avidflyer]

What if you remove the curtis valves, and replace with a short 1/8" pipe nipple with a cap on the end of it. Fill the tank, slosh it around, remove the cap, and catch the fuel in a funnel. Or slide a hose over the nipple and pinch the hose off with a vice grip plyers so it doesn't leak till you are ready to drain it out. Or you could remove the finger strainers and put a 1/4 pipe nipple there and do the hose thing as well. Would need the back of the plane higher in the air with the wing folded so it would drain out. JImChuk